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Why does the Aggregate Demand Curve slope downward?
Gari Jenkins
The aggregate demand curve shows the relationship
between the price level and output.
 The horizontal axis (Y) measures total economic
output or GDP (the demand for goods and services
by all sectors of the economy).
 The vertical axis (P) uses the overall price level
for the economy as a measure of prices / price index.
The aggregate demand curve slopes downward,
indicating that aggregate demand increases as the
price level falls ie an inverse relationship between
prices and output. (P  1/Y)
The Aggregate Demand slopes downward for several 3 main reasons.
Assume an increase in prices throughout . .
The Interest Rate Effect
Higher prices cause market interest rates to increase as lenders try to protect themselves from rising inflation
rates. Increases in interest rates cause investment to decline (all things being equal) as the cost of borrowing
rises. This reduces the Aggregate Expenditure and hence the output, through the multiplier effect.
As P  M/p  r  I AE  AD  Y . . . . Therefore, P  Y
M0/p1 M0/p0
p1 > p0
AE = C+I+G+X
r1
r0
AE’ = C+I’+G+X
y1
I1I0
/p
If we now take the equilibrium position for P & Y (ie
before we raised the price), we can plot this priceoutput pair on the diagram as shown (p0,y0)
.
After an increase in prices, we ended up at (p1,y1).
Again we can plot this. Already we can see the
downward sloping effect. If we did this for all
possible outcomes, we would end up with the curve
as above

(p1,y1)

(p0,y0)
The Wealth Effect
As the price level rises, the real value of money decreases and people find that they are poorer.
Reality PRINCIPLE
What matters to people is the real value of money or income–its purchasing power–not the face value of
money or income.
Higher prices lead to a decline in the market value of stocks, bonds, and other types of wealth. Changes in
the value of wealth impacts the level of consumption, a component of aggregate demand (GDP). With
higher prices we can expect consumption to fall due to the real balance effect.
As P  C AE  Y . . . . .Therefore, P  Y
The Net Export Effect
Higher domestic prices increase the price of exported goods sold in foreign markets. Furthermore, the
relative prices of imported goods fall, leading domestic consumers to substitute part of their consumption in
favour of the relatively cheaper imported goods. Assuming constant exchange rates, the overall impact of
higher domestic inflation is to decrease net exports, further reducing aggregate demand.
As P  X AE  Y . . . . .Therefore, P  Y
In summary, higher prices cause aggregate demand to decline as three important components of
aggregate demand are directly affected: consumption, investment, and net exports.
Factors That
Factors That Decrease
Increase Aggregate Aggregate Demand
Demand
Decrease in taxes
Increase in taxes
Increase in
government
spending
Decrease in
government spending
Increase in money
supply
Decrease in money
supply